Celtics head coach Brad Stevens told reporters on Friday that an MRI on small forward Gerald Wallace‘s knee revealed a torn meniscus, knocking him out indefinitely. Wallace had missed just one game all season, averaging 5.1 points, 3.7 rebounds, 2.5 assists and 1.3 steals while shooting 50.4% from the field.

The 6’7″ Wallace is in his first season in Boston, his 13th in the NBA, after being acquired from the Nets in the offseason. His offensive production is down significantly from his peak years and he’s playing only 24.4 minutes per game, his lowest average since he joined the Bobcats through the expansion draft prior to his fourth pro season. But the 2006 league leader in steals, a former All-Defensive First Team selection, is still a strong defensive presence, and the Celtics will surely miss his intensity on D.

Wallace, somewhat predictably, struggled to adjust to his sixth man role on a rebuilding team, and was vocal about what he perceived to be a lack of effort on the part of some of his younger teammates. Stevens said that he had been playing through the pain for some time, but in his last game, the 800th regular season game of his NBA career, he recorded his first double-double of the season, with 12 points and 10 rebounds.

Wallace’s injury is just the latest in a tough stretch for the Celtics who, at 20-39, are firmly out of playoff contention. Shooting guard Avery Bradley hasn’t played since February 9 with an ankle injury, power forward Jared Sullinger has missed the last three games with a concussion, and rookie big men Vítor Faverani and Kelly Olynyk both sat out Wednesday’s win over Atlanta with minor ailments.

Celtics Sign Babb to 10-Day Contract

Also on Friday, the Celtics officially announced the signing of shooting guard Chris Babb to a 10-day contract. Babb played his first two college seasons at Penn State and was part of the Nittany Lions team that won the NIT championship in 2009. He then transferred to Iowa State, and was named to the Big 12 All-Defensive Team in his senior season. He went undrafted and was signed by the Celtics for a short time in training camp.

Babb has played this season with Boston’s D-League affiliate, the Maine Red Claws, where he’s averaged 12 points, 6.2 boards, 3.4 assists and 1.2 steals. He will be eligible to make his NBA debut in the Celtics’ next game, Saturday against the Eastern Conference-leading Indiana Pacers.